1. Field of the Invention
The present invention relates generally to radio communications. Particularly, the present invention relates to improving a communication receiver""s immunity to interference.
2. Description of the Related Art
There are multiple types of cellular telephone systems in operation. These systems include the advanced mobile phone system (AMPS) and two digital cellular systems: time division multiple access (TDMA) and code division multiple access (CDMA).
Cellular systems operate by typically locating multiple antennas in the center of a cell covering a geographic region. The AMPS cells are separate and distinct from the CDMA cells so that the cells of each system overlap. This makes it likely that the antenna for one system""s cell may be located in a cell of another system. Likewise, within a particular system (e.g., AMPS, CDMA, TDMA), there are at least two service providers within a given area. These providers often choose to place cells in different geographical locations from the competitor. Hence, there are situations where a telephone on system xe2x80x98Axe2x80x99 might be far away from the nearest system xe2x80x98Axe2x80x99 cell while close to a system xe2x80x98Bxe2x80x99 cell. This situation means that the desired receive signal might be weak in the presence of strong multi-tone interference.
The intermixing of system antennas can cause problems for a mobile station that is registered in one system, such as the CDMA system, and travels near another system""s antenna, such as an AMPS antenna. In this case, the signals from the AMPS antenna can interfere with the CDMA signals being received by the mobile station due to the proximity of the mobile station with the AMPS cell or the higher power of the AMPS forward link signal. This is referred to in the art as xe2x80x98jammingxe2x80x99.
It is frequently the case in an AMPS system for carriers to xe2x80x98jamxe2x80x99 a competitor""s system unintentionally. One of the goals of a cellular carrier is to provide a high signal-to-noise ratio for all the users of their system by placing cells close to the ground or near their users and radiating the FCC power limit for each channel. This technique provides for better signal quality for one carrier""s system at the expense of interfering with the competitor""s system.
One way to improve the immunity of a receiver to interference or jamming is to increase the current to the receiver. This is not a practical solution, however, for a mobile station that relies on battery power. Increasing the current would drain the battery more rapidly, thereby decreasing the talk and standby time of the mobile station. Additionally, a detector is typically used to detect the presence of the jamming signal. However, by the time the jamming signal has been detected and the linearity of the receiver increased, the jamming signal may no longer exist.
There is a resulting need to quickly control a mobile station""s immunity to interference without greatly increasing power consumption.
The present invention provides control of the linearity of a low noise amplifier in a receiver of a mobile station. This provides the desired level of immunity to interference while reducing the average current consumption of the receiver. In a battery powered device, reducing the current consumption has the effect of increasing talk and stand-by times.
The present invention encompasses a process for controlling the linearity of a low noise amplifier. The low noise amplifier is first enabled. It is then determined if a predicted level of interference will produce an acceptable bit error rate or other signal error measurement.
If the predicted level of interference is not going to be acceptable, the low noise amplifier is adjusted to a high level of linearity. If the predicted level of interference is acceptable, the low noise amplifier is set to a low level of linearity.